Cluster vs stratified sample

Stratification is often used to create strata such that units within strata are more alike in terms of the variable of interest. As a result, variability within strata is greatly reduced and it is this variability that determines the variability of an estimator. Naturally occurring clusters also often have units that are more like. However, the variability of an estimate is mostly determined by the between cluster variability. Which of the following is true? Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer. Because variability in cluster sampling is often large between clusters, estimates from cluster samples tend to be more variable than a those from an SRS b Because variability in cluster samples is often small within clusters, similar to stratified sampling, the variability of an estimator from a cluster sample will be small. C Cluster samples and stratified samples are both time consuming and costly and should be avoided